1. Field of the Invention
The invention relates to a linear drive apparatus including a cylindrical casing having a longitudinal slot, a driving unit arranged for a reciprocating movement in an inner chamber of the cylindrical casing and having a projection projecting through the slot, which slot is sealed off at least at its outer side by an outer sealing strip extending over the length of the casing, which sealing strip is lifted off the longitudinal slot at the location of the projection and is led through a bracket mounted to the projection.
2. Description of the Prior Art
Linear drive apparatuses of the design set forth above are generally known. The driving unit located inside of the cylindrical casing of a known design of such a linear drive apparatus is a piston, which at its face end is sealed against the inner space. The longitudinal slot is also sealed at its inner side by a sealing strip. The moving of the piston is produced by pressure differentials at the two face end sides of the piston.
A further design of a linear drive apparatus is known in which a helical spindle is located inside of the casing, which moves upon a rotating an element having a thread in the longitudinal direction.
When the driving unit moves, a small amount of abrasion is produced. In spite of the outer sealing strip it is possible that abraded matter enters into the surroundings of the area at which this sealing strip is lifted off the edges of the longitudinal slot. For normal operations this occurrence is not disturbing. When the piston is driven by pressurized air, this pressurized air contains also small contaminations which can also reach the surroundings. On the other hand, it is also possible that specifically at the area, where the sealing strip lifts off, contaminations can move from the surroundings of the linear drive apparatus into its inner space. Such contaminations can be for instance dust or particle-like matter. When the linear drive apparatus is to be operated in a surrounding in which solvents are used, it is also possible that such solvents enter the inner area of the cylindrical casing and negatively influence or even destroy lubricating matter used for decreasing friction. The positions can also lead to a getting worse of the sealing property of the sealing strip.